OSPF LSA Types Lab
LSA Types 5 in Stub Area
In the next part we are going to configure Area 1 as a Stub Area. To configure a stub area we have to type below commands on all routers in that stub area:
| R2, R3, R4: router ospf 1 area 1 stub |
A warning message “Warning: Router is currently an ASBR while having only one area which is a stub area” appears when we configure stub area on R3. Remember that R3 is currently an ASBR and redistributed routes are not accepted in stub areas.
We can check to see Area 1 is now a stub area with the “show ip ospf” command:
LSA Type 5 is not allowed in stub area (only Type 1, 2, 3 allowed in Stub area) so we don’t see Type 5 in R4 OSPF database:
As we can see in the output above, R4 has a Link ID of 0.0.0.0 advertised by R2. This is the default route to reach outside networks. It is injected into the area by the ABR (R2)
LSA Types 4 & 5 are also removed from R7:
In conclusion, LSA Type 5 is not supported in Stub area. But remember Stub area does support LSA Type 3.
LSA Type 5 in Not-So-Stubby-Area
Type 5 is not allowed in Stub area so we have to convert Area 1 into Not-So-Stubby-Area (NSSA)
Configure Area 1 as Not-So-Stubby Area:
| R2, R3, R4: router ospf 1 no area 1 stub //Before configuring Area 1 as NSSA we need to disable stub area first area 1 nssa |
When Area 1 becomes NSSA, ASBR is allowed to redistribute external routes but LSAs Type 5 are still not allowed in NSSA areas so the NSSA ASBR (R3) generates a type 7 LSA instead, which remains within the NSSA. This type 7 LSA gets translated back into a type 5 by the NSSA ABR (R2).
Let’s check the OSPF databases of some routers:
On R7 only Type 5 LSA exists. R2 is the only router we can see both Type 5 and Type 7:
Check R4, only Type 7 exists:
Redistributed routes appear as O N2 in NSSA. For example on R4:
while redistributed routes appear as O E2 on R7:
Fantabulous, never seen such a great explanation….
One thing to add after changing Area 1 as NSSA the Link ID in LSA 4 has changed from 3.3.3.3 to 2.2.2.2 on router 7 and also forward address changed to 23.23.23.3, any guess ?
Awesome explanation. I’ve simulated your configuration and was able to follow through.. This ‘s definitely the best Tutorial of LSA Type that I have seen so far.. Thank you so much.
very good stuff, well thought out and demonstrated
Excellent explanation thanks.
gracia!!!
Thank you !!!
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Excellent work
Great tutorial
Excellent, but I confused little about LSA type 2.
Great tutorial!
good stuff
Nice Explanation,
Question : Why does RS have both LSA-5 and LSA-7, while it’s configured as NSSA?
Nice Explanation,
Question : Why does R2* have both LSA-5 and LSA-7, while it’s configured as NSSA?
PHX, because it its also ABR, has special responsibility for distributing information between Areas and belongs to two areas.
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FANTASTIK EXPLANATION
Excelent!! Great explanation!! Thanks a lot. sometimes I was confused about lsa type 4 and 5
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Simply Outstanding and Awesome Tutorial on LSA Types.
Excellent! Very good tutorial
I was contemplating on purchasing membership. but the GNS topology file looks very old. Is it possible to have one for the latest GNS3 2.1.x release?
https://gns3.com/community/discussion/gns3-0-8-3-net-topology-file-com
thanks for the explanation, very good.
How can I open this .net file?
Cant anybody let me know how I can use with IOU Web
That was mind blowing !!!!